Reading a csv file in python

Question

I want to open and read file Mappe1.csv but it is not working. I am using Python 3.6.5 Anaconda. I do not know what I am doing wrong. Any ideas?

File Mappe1.csv contains:

A;B;C
1;4;7
2;5;8
3;6;9

The python code for opening Mappe1.csv looks like the following:

import csv


class CSVAdapter:
    def read_csv(self):
        with open("C:/Users/User/PycharmProjects/General/DesignUploader/Mappe1.csv") as file:
            dialect = csv.Sniffer().sniff(file.read(1024))
            csv_file = csv.reader(file.readlines(), dialect, quotechar='"')
            print("A")
            csv_file_list = []
            for row in file:
                print("B")
            for row in csv_file:
                print("C")
                csv_file_list.append(row)
        return csv_file_list

The printout is "A" only. "B" and "C" does not get printed which leads me to the conclusion that the file was not read correctly.

Are there any python/windows settings required to allow Python to read a file?

Thank you for your help!

That call to `read(1024)` reads the whole file, leaving nothing left to read. Then you call `readlines()`, which also reads the whole file, or would if there were anything left. Then `for row in file:` also reads the whole file. And, of course, so does `for row in csv_file:`. — abarnert, Jul 24 '18 at 22:45

Andrej Kesely · Accepted Answer · 2018-07-24T22:25:39.497

You need to supply to csv.reader file object, not file.readlines(). If you want to print Bs, you need to seek to the beginning of file, similar with the Cs.

import csv

def read_csv():
    with open("data.csv") as file:
        dialect = csv.Sniffer().sniff(file.read(1024))
        csv_file = csv.reader(file, dialect, quotechar='"')

        print("A")
        csv_file_list = []

        file.seek(0)

        for row in file:
            print("B")

        file.seek(0)

        for row in csv_file:
            print("C")
            csv_file_list.append(row)
    return csv_file_list

print(read_csv())

Prints:

A
B
B
B
B
C
C
C
C
[['A', 'B', 'C'], ['1', '4', '7'], ['2', '5', '8'], ['3', '6', '9']]

score 0 · Answer 2 · answered Jul 24 '18 at 22:32

csv.reader takes a file object as first parameter, not a list which is what file.readlines() returns.

So your line:

csv_file = csv.reader(file.readlines(), dialect, quotechar='"')

should be:

csv_file = csv.reader(file, dialect, quotechar='"')

your for loop to print('B') should be:

for row in file.readlines():
    print('B')

your for loop to print('C') should work fine like it is although it is worth noting that you could directly set csv_file_list = list(csv_file). And you should reset your file to the first line with:

file.seek(0)

T.Woody · Answer 3 · 2018-07-24T22:37:23.103

In your code, you are only printing A, B, or C. Try printing the whole line instead. You will see that the row in cvs_file is an object where we are only accessing one part of it. From the docs, see the example:

 >>> import csv
 >>> with open('eggs.csv', newline='') as csvfile:
 ...     spamreader = csv.reader(csvfile, delimiter=' ', quotechar='|')
 ...     for row in spamreader:
 ...         print(', '.join(row))
 Spam, Spam, Spam, Spam, Spam, Baked Beans
 Spam, Lovely Spam, Wonderful Spam

From this example, try:

 for row in csv_file:
     print(','.join(row))

instead.

Finally, you will want to change the way the files are being read. Your cvs_files is using delimiter of ;. Try that instead of the dialect. And your file does not actually have any property row. You will need to

lines = file.readlines()

score -1 · Answer 4 · edited Nov 25 '22 at 08:40

This is alternative solution. I use the Pandas tool for reading CSV file when working with data. The code is actually very simple, and outputs the answer into a Pandas DataFrame data structure. For me, tt is cleaner to read extracted information and easier to process than the csv tool.

Here is snippet:

import pandas

df = pandas.read_csv('C:/Users/User/PycharmProjects/General/DesignUploader/Mappe1.csv')
print (df)

Reading a csv file in python

4 Answers4